1. Field of the Invention
The present invention relates to an electron beam indicator tube of high luminance, for example, for a large-screen display having a two-dimensional arrangement of a plurality of such electron beam indicator tubes.
2. Description of the Prior Art
There has been proposed a display comprising a large screen having a two-dimensional arrangement of luminous indicator cells each having fluorescent trios each consisting of cathodes, first grids, second grids and, for example, red, green and blue fluorescent layers.
FIGS. 10, 11 and 12 illustrate an exemplary electron beam indicator tube, i.e., a luminous indicator cell, integrally incorporating two sets of fluorescent trios. This luminous indicator cell comprises a glass case 1, two sets of fluorescent trios 3 (3A and 3B) are formed in the glass case 1 and each consist of red, green and blue fluorescent layers 2R, 2G and 2B which have the same areas. There are three linear cathodes K (K.sub.R, K.sub.G and K.sub.B) disposed, respectively, opposite to the fluorescent layers 2R, 2G and 2B of each of the fluorescent trios 3A and 3B. There are electrode units 4 (4A and 4B) each consisting of three first grids (control grids) G.sub.1 (G.sub.1R, G.sub.1G and G.sub.1B) and a common second grid (accelerating grid (G.sub.2. There is also a separator structure 5 formed of a conductive material so as to enclose the fluorescent layers 2R, 2G and 2B of each of the two sets of fluorescent trios 3. Rectangular, meshy electron beam transmission apertures 6R, 6G and 6B which have the same shape as the fluorescent layers 2R, 2G and 2B are formed in the second grid G.sub.2 at positions, respectively, corresponding to the first grids G.sub.1R, G.sub.1G and G.sub.1B.
An anode lead 7 is connected to a conductive getter container 8 mechanically supported on and electrically connected to part of the separator structure 5, and which projects outside through a chip-off tube 9 which is attached to the backside of the glass case 1.
In this luminous indicator cell disclosed in Japanese Patent Application Nos. 60-191703 and 59-256357, a fixed anode voltage in the order of 8 kV is applied through the anode lead 7 and the separator structure 5 to the red, green and blue fluorescent layers 2R, 2G and 2B of each of the fluorescent trios 3. A voltage, for example, in the range of 0 to 5 V is applied to the first grids G.sub.1. A fixed voltage, for example, in the range of 30 to 50 V is applied to the second grid G.sub.2, and the voltage applied to the first grids G.sub.1 is selectively removed and supplied to an indicator.
In the foregoing known luminous indicator cell, the fluorescent layers are arranged contiguously with a small gap therebetween, and a small current is supplied to the separator structure 5 which has an anode potential which causes the entire area of the fluorescent layer to compensate for variations attributable to irregularities caused during assembly of the luminous indicator cell. The temperature of the opposite ends of the linear cathodes K drops during operation and the opposite ends of the linear cathodes K are unable to discharge sufficient thermions and, consequently, the respective upper and lower ends of the fluorescent layers 2R, 2G and 2B have low luminance.